Polyfit on a 3d plot

Hello everyone,

i'm trying to create a matrix containing the coefficient of a 3rd degree polyfit on each rows with the shape 13000x4.

For that, i have the following data shape:

Time : 13000x1 %time corresponding actually to the number of rows

Position : 13000x4 %the position is just for the sake of the plot (position of the sensor in reality). The four columns have each a constant value over the 13000 rows

Displacement: 13000x4 %measurement in global Z of four sensors.

(see image attached) My purpose is to "slice" the 3d plot at every time "t" (13000 times) and apply a polyfit on the 4 red cross (x = position, y = displacement) in order then to evaluate the curve to obtain the 2 yellow points. Ultimaly, i want to recreate a line out of the yellow points.

Up to now, i was only able to extract a few sets of points (red crosses) at a given time manually. I don't know how to reshape the matrix without creating 13000 submatrix and names associated.

I hope that my explanations are clear enough and that you can give me a little help on that one.

Thanks in advance

Fabio

Answer 1

[dpb]

That's fairly simple, just loop over the displacement array with a set of the position data to compute that set of coefficients and evaluate them where needed.

nD=size(D,1);                       % the important size of D
NewD=zeros(nD,2);                   % for the new points -- could augment D instead but this is simpler
NewP=[300,2400];                    % GUESS FOR THE NEW POINT LOCATIONS -- SET AS DESIRED
for i=1:nD                          % iterate over rows of D
  b{i}=polyfit(P(1,:),D(i,:),3);    % compute polyfit coefficients for each (hold in cell array)
  NewD(i,:)=polyval(b{i},newP);     % evaluate and save new positions
end

leaves you with the additional data points at the two positions -- just draw them directly or you could add to the original D array...

[Fabio Carton]

Thank you very much!! it was pretty much what i was looking for.

I acknowledge that it can appear easy but i'm still a learner and some loops are still tricky for me.

All the best